Creepage spark type plug having low voltage igniter seal



Sept. 26, 1967 G. F. RADEMACHER CREEPAGE SPARK TYPE PLUG HAVING LOWVOLTAGE IGNITER SEAL Filed June 25, 1965 f/fl United States Patent C3,344,304 CREEPAGE SPARK TYPE PLUG HAVING LQW VOLTAGE IGNITER SEALGustav F. Rademacher, Davison, Mich., assigner to General MotorsCorporation, Detroit, Mich., a corporation of Delaware Filed June 23,1965, Ser. No. 466,334 9 Claims. (Cl. 313-131) ABSTRACT F THE DISCLSUREThis invention relates to a low voltage igniter having a conductiveglass seal positioned `between the firing tip portion of the centerelectrode and the lower portion of the tubular semiconductor whichencircles the tiring tip portion. This conductive metal-glass sealcauses the spark to originate at the desired location at the end of thetiring tip portion of the center electrode thereby eliminatingfracturing of the center electrode at points above the end of the tiringtip.

This invention relates to a low voltage igniter, and more particularlyto a low voltage igniter employing a flush gap between the centerelectrode and the ground electrode.

It is well recognized that low voltage igniters have a short life due tothe rapid erosion of the center electrode and/ or the semiconductor.Erosion which causes fracturing of the center electrode and/or thesemiconductor is particularly deleterious because the fractured piecescan cause extensive damage to the turbine.

In low voltage igniters employing a shielded or nonush gap between thecenter electrode and the ground electrode, that is, where the sparkingend of the center electrode has an enlarged head below the lower surfaceof the semiconductor, the problem commonly encountered is theundercutting by erosion of the center electrode enlarged head.

In low voltage igniters employing a ush gap between the center electrodeand the ground electrode, the problem of fracturing the center electrodestill exists despite the absence of the enlarged head below the lowersurface of the semiconductor. Ideally, the center electrode and thesemiconductor are in intimate contact with eac-h other along the shaftyof the lower portion of the center electrode thereby resulting insparking at the designed location; namely, where the electrode emergesat the face of the semiconductor. Normally, however, during themanufacture of ilush gap igniters the center electrode is insertedthrough the semiconductor material thereby requiring a certain degree ofclearance between these two parts. This clearance space causes thesparking to occur in places other than the designed location.Frequently, especially in the presence of gap quenching -fuel oil, thespark originates then at some point above the tip where good contactexists. This type of sparking which occurs in the clearance space-between the semiconductor and the center electrode instead of on thefiring tip end of the center electrode results in ring-shaped erosionabove the electrode tip, fracture of the semiconductor and/ or fractureof the center electrode tip.

It is a basic object of this invention to provide an improved lowvoltage igniter having a ush gap design in which the spark originates atthat portion of the center electrode which emerges at the face of thesemiconductor. It is another object of this invention to provide aconductive seal means to ll the clearance space between thesemiconductor and the center electrode to prevent the spark fromoriginating in the clearance space between the semiconductor and thecenter electrode. It is still another object of this invention to reducering-shaped erosion above the electrode tip Iand the accompanyingfracturing of the center electrode tip.

These and other objects are accomplished by filling the clearance spaceseparating the semiconductor from the center electrode with a conductivemetal-glass seal which hermetically bonds the center electrode to thesemiconductor. Specifically, in the illustrated embodiments disclosedherein, the low voltage igniter comprises a metal shell, the lower endthereof constituting the ground electrode and a tubular semiconductorpositioned within and in intimate electrical contact with the groundelectrode. A center electrode is positioned within the tubularsemiconductor and is sealed to the semiconductor by means of anelectrical conductive metal-glass seal. When this low Voltage igniter isenergized, the spark will originate on that portion of the centerelectrode which emerges at the face of the semiconductor. Theglass-metal seal causes the spark to originate at the desired locationat the end of the center electrode there'by eliminating fracturing ofthe center electrode at points above the firing tip.

Other objects `and advantages of this invention will be apparent fromthe following detailed description, reference `being made to theaccompanying drawings wherein several preferred embodiments of thisinvention are shown.

In the drawings:

FIGURE 1 is a side View of an improved flush gap low voltage igniterplug having a cylindrical center electrode partly in cross section andpartly in elevation;

FIGURE 2 is a side view of a firing tip portion of an improved flush gaplow voltage igniter having a cylindrical center electrode with anenlarged end portion partly in cross section and partly in elevation;

FIGURE 3 is a side View of a tiring tip portion of au improved flush gaplow voltage igniter having an enlarged center electrode tip portionpartly in cross section and partly in elevation;

FIGURE 4 is a side View of the flush gap low voltage igniter plug duringthe manufacture thereof just prior to pressing the insulator intoposition partly in cross section and partly in elevation.

Referring to FIGURE 1 of the drawings, the low voltage igniter 10comprises a conventional outer tubular metal shell 12 having the lowerend portion thereof constituting an annular ground electrode 14. Theground electr-ode 14 may be made of any suitable high temperatureerosion resistant metal or metal alloy. Inconel containing approximately76% nickel, 16% chromium and 6% iron was used in the preferredembodiment.

Positioned within the ground electrode 14 is a tubular semiconductor 16.Semiconductor materials presently being used in low voltage igniters maybe used in this invention. The patent to Edwards 3,052,814 describes indetail the silicon nitride-bonded silicon carbide semiconductor whichperrorms satisfactorily. The semiconductor 16 has an inwardly extendinglower portion 18 thereof in electrical contact with the inwardlyextending lower portion Ztl of said ground electrode 14. rThe internaldimensions of the tubular semiconductor will be hereinafter discussed.The vertically extending portion of the semiconductor 16 is separatedfrom the ground electrode 14 by a glass seal 22. Glass seal compositionstypically used in spark plugs and igniters may be used for thisapplication. The composition of the glass seal 22 used in the preferredembodiment consists of 65% S102, 25% B203, 5% A1203 and 7% NaZO,however, this invention is not limited to this composition.

Positioned within the tubular semiconductor 16 is the center electrode24. The tiring tip portion of the center electrode may be of any hightemperature erosion resistant metal or alloy, such as Inconel, tungsten,platinum and/ or iridium. The center electrode 24 may be of a onepiececonstruction of a single metal or it may consist of two parts, thetiring tip portion comprising a high temperature erosion resistant metalor alloy and the upper portion comprising another metal such as Kovar.Kovar is a low expansion iron base alloy containing 28 to 30% nickel, 15to 18% cobalt and fractional percentages of manganese. The shape of thecenter electrode 24 will be hereinafter discussed.

The clearance space between the semiconductor 16 and the lower portionof the center electrode 24 is filled with a conductive metal-glass seal26. The seal 26 is hermetically bonded to semiconductor 16 and centerelectrode 24. The function of the conductive metal-glass seal 26 whichhermetically fills the clearance space between the center electrode andthe semiconductor is to direct the sparks from the tip 28 of the centerelectrode 24 to the lower surface 30 of the semiconductor 16 and to theground electrode 14. The conductive glass seal 26 prevents ignitershaving the flush gap design from sparking at points on the centerelectrode 24 above the ring tip portion 28. The spark, as a result,originates at the designed location and eliminates the problem of centerelectrode fracturing which can cause expensive turbine damage.

The composition of the metal-glass seal used in the preferred embodimentis 50 weight percent tungsten and 50 weight percent glass. The chemicalanalysis of the glass used was 65% SiOZ, 25% B203, 5% A1203 and 7% NaZO.Suitable glasses having different chemical analysis may be used. Inaddition, a metal-glass seal may contain binders and/ or iiuxes. Othersuitable metals which may be used in the conductive metal seal arenickel, copper, platinum, and iridium. The concentration of the metal inthe metal-glass seal may vary from 25 weight percent up to 90 weightpercent. The minimum amount of metal required in the metal-glass seal isapproximately 25 weight percent. This amount is necessary in order toinsure suicient conductivity so that current may travel across themetal-glass seal. Glasses having metal concentrations below this amountdo not have suicient conductivity, and as a result, are insulators whichrequire the spark to jump across the seal. If the metal-glass seal isnon-conductive or insulative, a higher voltage is required for the sparkto jump across this metal-glass gap from the center electrode to thesemiconductor. The upper limit of the metal concentration isapproximately 90 weight percent. The maximum amount of metal in such acase is governed by the ease of ilow of the metal-glass seal, and it hasbeen found that it requires or more of glass in order to insuresufficient owability of the metal-glass mixture. Mixtures having morethan 90% metal or less than 10% glass were found to have insufiicientowability for the purposes of this invention.

The internal dimensions of the tubular semiconductor 16 depend upon theshape of the lower portion of the center electrode 24. The semiconductor16 and the center electrode 24 should have dimensions which cooperate toform a constriction, thereby providing a passageway conducive for theiluid metal-glass mixture to ow downward and ll the clearance spacecompletely near the opening in the tiring tip region between 30 and 28.For example, as shown in FIGURE 1, where the center electrode is auniform cylinder, it is necessary to have a semiconductor design inwhich the internal diameter dimension gradually `decreases as the firingtip portion is approached to form a constriction about the centerelectrode. Decreasing the internal diameter of the tubular semiconductorfrom a given width 17 to a narrower width 19 and a still narrower width21 about the firing tip portion of the center electrode enables thefluid metalglass mixture 16 to flow uniformly about the firing tipportion of the center electrode between 28 and 30.

As shown in FIGURE 2, the firing tip portion 34 of the center electrode36 is in the form of an enlarged cylinder. The conductive metal-glassseal 38 is positioned between the semiconductor 40 and the centerelectrode 36 and the firing tip portion 34. The semiconductor 40 has auniform internal diameter. The outer electrode 36 starts with thediameter 37 which is increased gradually as the firing tip portion isapproached as shown at 39 until it has a larger diameter as indicated at41. The constriction formed by the electrode tapering along the slope ofthe electrode as shown at 39 and the vertical inner wall of thesemiconductor 40 provides the necessary constriction which insuresadequate llowability in the clearance area about the firing tip portion34.

The inwardly extending lower exterior portion 43 of the semiconductor 40is in electrical contact with the inwardly extending portion 45 of theground electrode 42. Glass seal 44 is positioned between the verticalextending portions of the semiconductor 40 and the ground electrode 42.

FIGURE 3 shows a tiring tip assembly in which the center electrode andthe semiconductor have still another configuration. The relationshipbetween the ground electrode 52, the glass seal 54 and the semiconductor56 is the same as described in FIGURES 1 and 2. The semiconductor 56 hasa lower inwardly extending portion 58. The center electrode 60 has anenlarged tiring tip portion 62. The ring tip portion 62 has an inwardlyextending end portion 64. The conductive metal-glass seal 66 ispositioned between the semiconductor 56 and the center electrode 60 andthe firing tip portions 62 and 64. The constriction is formed by theinwardly tapered lower portion 64 of the center electrode 6) and theinwardly tapered lower end 58 of the semiconductor 56. The tapered endportions of the firing tip 64 and the semiconductor S8 are not paralleland tend to come closer together at the bottom of the igniter. lIn otherwords, the distance between the semiconductor 58 and the centerelectrode firing tip portion 64 is greater at point 68 than it is atpoint '70. This constriction insures adequate metal-glass flow about thefiring tip end portion 64 of the center electrode 60.

FIGURES 2 and 3 show a center electrode having an enlarged mass at thefiring tip in order to extend the life of the igniter. The conductivemetal-glass seal functions in the same manner in FIGURES 1, 2 and 3,regardless of the shape of the firing tip portion of the centerelectrode. The conductive metal-glass seal fills the clearance space,which has been enlarged in FIGURES 2 and 3 for illustrative purposes,between the center electrode and the semiconductor and insures intimatecontact between the semiconductor and the center electrode at the end ofthe firing tip, which is the designed tiring location. When the sparkingoccurs at the designed location, that is, at the end of the firing tipportion of the center electrode, there is no fraeturing of the centerelectrode at points above the tiring tip end.

In the manufacture of a low voltage igniter 10' having a llush gapdesign, the following procedure is used. An igniter shell 12 ispositioned in an upright position, thereby resting on the groundelectrode 14 as shown in FIG- URE 4. The semiconductor 16 is insertedinto the top of the shell 12 and positioned so that the semiconductorportion 18 is in electrical Contact with the inwardly extending portion20 of the ground electrode 14. The center electrode 24 is then insertedin the shell 12 and positioned so the lower end of the center electrode24 is positioned within the tubular semiconductor 16. A measured amountof the conductive metal-glass powder mixture 26 is inserted between thesemiconductor 16 and the center electrode 24 and tamped. The quantity ofthe conductive metal-glass 26 used is not critical as long as there issuiiicient metal-glass seal available in the sparking region. Normally,however, a large portion of the clearance space between thesemiconductor 16 and the center electrode 24 is filled with theconductive metal-glass mixture 26. Glass powder 22 is then insertedbetween the semiconductor 16 and the ground electrode 14 as well as ontop of the metal-glass powder 26. The insulator 11 is then inserted inthe shell and positioned on top of the glass powder 22. This assembly isthen placed in a warm oven and the temperature of the oven `is raised tol700 F. The assembly is kept at a temperature of 1700 F. for 3 minutesin order to melt the glass powder and the glass in the metal-glasspowder mixture. As soon as the assembly is removed from the oven,pressure is applied to the insulator 11 forcing the fluid metal-glass 26mixture to iill the clearance space 27 around the iiring tip portionofthe center electrode. FIGURE 1 shows the position of the insulatorafter the metal-glass mixture 26 has been forced into the clearancespace. The iiuid glass 22 is forced into the space separating the shell12 from the insulator 11 and the space between the ground electrode 14and the semiconductor 16.

While the invention has been described in terms of preferredembodiments, it is to be understood that the scope of the invention isnot limited thereby except as deiined in the following claims.

I claim:

1. A low voltage igniter plug having a flush gap tiring tip assemblycomprising an outer annular ground electrode, a tubular semiconductorpositioned longitudinally within said ground electrode and being inelectrical contact with said electrode, a center electrode positionedlongitudinally within said tubular semiconductor, conductive sealingmeans positioned between said center electrode and said semiconductorand being bonded thereto, said sealing means directing a spark from thelower end of said center electrode when said igniter plug is energized.

2. A low voltage igniter plug having a ilush gap tiring tip assemblycomprising an outer annular ground electrode, a tubular semiconductorpositioned longitudinally within said ground electrode and being inelectrical contact with said electrode, a center electrode positionedlongitudinally in said tubular semiconductor, a conductive metal-glassseal positioned between said center electrode and said semiconductor andbeing bonded thereto, said conductive metal-glass seal directing a sparkfrom the lower end of said center electrode when said igniter plug isenergized.

3. An igniter plug as described in claim 2 wherein said conductive metalseal comprises 25 weight percent to 90 weight percent of a metal powder.

4. An igniter plug as described in claim 2 wherein said conductivemetal-glass seal comprises a metal taken from the group consisting oftungsten, copper, nickel, iron, Kovar, platinum and iridium.

5. A low voltage igniter plug comprising a tubular metal shell having alower end constituting an annular ground electrode, said groundelectrode having a lower portion extending inwardly, a tubularsemiconductor positioned within said tubular metal shell and having aninwardly extending annular lower portion in electrical contact with theinwardly extending portion of said ground electrode, a center electrodepositioned in said semiconductor, a conductive metal-glass sealpositioned between said center electrode and said semiconductor andbeing bonded thereto, said conductive seal directing -a spark from thelower end of said center electrode when said igniter plug is energized.

6. A low voltage igniter plug comprising a tubular metal shell having alower end constituting an annular ground electrode, said groundelectrode having a lower portion extending inwardly, a tubularsemiconductor positioned within said tubular metal :shell and having aninwardly extending annular lower portion in electrical contact with theinwardly extending portion of said ground electrode, a center electrodepositioned in said semiconductor, -a conductive metal-glass sealpositioned between said center electrode and said semiconductor andbeing bonded thereto, said center electrode and said semiconductor beingin spaced relationship with each other to form a vconstriction adjacentthe firing tip end of the center electrode thereby insuring that saidseal completely iills the space between the semiconductor and the firingtip end of the center electrode, said conductive seal directing a sparkfrom the lower end of said lower electrode when said igniter plug isenergized.

7. An igniter plug as dened in claim 6 wherein said semiconductor istapered inwardly toward said center electrode to form a constrictionbetween said semiconductor and said center electrode.

8. A low voltage igniter plug as described in claim 6 wherein saidcenter electrode is tapered outwardly toward said semiconductor to forma constriction between said semiconductor and said center electrode.

9. An igniter plug as dened in claim 6 wherein both said semiconductorand said center electrode taper inwardly in the tiring tip region toform a constriction between said semiconductor and said centerelectrode.

References Cited UNlTED STATES PATENTS 2,831,993 4/1958 entz S13-11.52,836,756 5/1958 Smits 313-137 X 2,867,740 1/1959 Segall 313-131 X2,874,321 2/1959 Summerer 313-131 X JAMES W. LAWRENCE, Primary Examiner.C. R. CAMPBELL, Assistant Examiner.

1. A LOW VOLTAGE IGNITER PLUG HAVING A FLUSH GAP FIRING TIP ASSEMBLYCOMPRISING AN OUTER ANNULAR GROUND ELECTRODE, A TUBULAR SEMICONDUCTORPOSITIONED LONGITUDINALLY WITHIN SAID GROUND ELECTRODE AND BEING INELECTRICAL CONTACT WITH SAID ELECTRODE, A CENTER ELECTRODE POSITIONEDLONGITUDINALLY WITHIN SAID TUBULAR SEMICONDUCTOR, CONDUCTIVE SEALINGMEANS POSITIONED BETWEEN SAID CENTER ELECTRODE AND SAID SEMICONDUCTORAND BEING BONDED THERETO, SAID SEALING MEANS DIRECTING A SPARK FROM THELOWER END OF SAID CENTER ELECTRODE WHEN SAID IGNITER PLUG IS ENERGIZED.